Andrew Mitchell is facing calls to quit as police insisted details of the chief whip's tirade against an officer were accurate.
The Tory enforcer was accused of shouting "learn your f****** place" after being stopped from cycling out of Downing Street's main gates and described officers as "plebs", according to The Sun.
Although the former shadow police minister has apologised for not treating the police with proper respect he has denied using some of the language reported.
Labour said Mr Mitchell was either accusing the member of Scotland Yard's Diplomatic Protection Group, SO6, of lying or he must have used the foul language, potentially an arrestable offence.
John Tully, chairman of the Metropolitan Police Federation, said: "I have it on good authority that the report in The Sun newspaper accurately reflects what happened." He added: "He should resign. As a Cabinet minister it's unacceptable for someone of his standing to use such disrespectful and abusive language to a police constable let alone anyone else."
David Cameron dodged questions about whether he planned to sack Mr Mitchell and condemned his behaviour as "wrong" and "inappropriate". The Prime Minister appeared tense when asked about the outburst during a visit to Greater Manchester Police headquarters to pay his respects to murdered Pcs Fiona Bone and Nicola Hughes.
"What Andrew Mitchell said and what he did was not appropriate. It was wrong and it is right that he has apologised," he said. "He has obviously apologised to me, but more importantly he has apologised thoroughly to the police and that needed to be done.
"Police do an outstanding job across our country. They do a very important job protecting places like Number 10 Downing Street and I am very conscious of the protection they give to me and my family and the work they do for everyone in public life. I am eternally grateful for that and the police should always have our respect and our help and support and that is very, very important."
Mr Mitchell made a personal apology to the officer involved by telephone as he tried to limit the damage from the episode. A Cabinet Office spokesman said the officer had accepted Mr Mitchell's apology. No formal complaint has been filed over the politician's behaviour.
Mr Tully later said Mr Mitchell had been warned by officers at the time and was likely to have been arrested if he had continued. He told Channel 4 News: "There is a written record of the incident in the officers' notebooks. I understand there is extensive CCTV coverage throughout Downing Street and in Whitehall. Clearly there isn't audio on that but I've got no reason to doubt the integrity of the officers." He added: "I understand that following his tirade to the officers he was warned and he desisted. I think had he continued he would have been arrested."